1. Field of the Invention
The present invention relates to an image processing apparatus for correcting the color of an image that is output from a printer, an image processing method therefor, and a program for generating image processing parameters.
2. Description of the Related Art
With the improved performance of image forming apparatuses in recent years, some image forming apparatuses have achieved an image quality equivalent to that of printing machines. However, the printing characteristics of an image forming apparatus are known to be changed by the influence of the installation environment. There has been a problem in that the temperature or humidity in the installation environment and the aging of the apparatus and parts replacement change the density and tint at the time of printing, and a stable print product cannot be obtained.
To solve this problem, an image forming apparatus generally employs a calibration technique so that a stable print product is output. The calibration technique is a technique for correcting the gradation characteristics of toner used for printing. The technique prints some patches having different gradations with known toner amounts, and measures the density of these patterns by using a scanner or a sensor connected to the image forming apparatus. The technique generates a correction look-up table (LUT) so that the result of the measurement coincides with a known target density. Applying the generated correction LUT at the time of printing enables obtaining a stable output suitable for the target density characteristics.
In addition to the above-described factors of the image forming apparatus, the change in the printing characteristics is greatly affected by the characteristics of paper used for printing. There are various types of paper used for printing, which differ in size, grammage, surface property, and paper chromaticity. Even with the same characteristics of the image forming apparatus, different paper characteristics (paper type) used for printing will cause different reproduction characteristics of the result of printing. Therefore, the image forming apparatus prepares a target value for each paper type, and performs calibration for correcting the reproduction characteristics so that the output value coincides with the target value, and stores a correction LUT generated each time calibration is executed. By performing calibration in this way, the image forming apparatus reduces the influence of the difference in paper (paper type) on the reproduction characteristics. In calibration, the image forming apparatus applies the correction LUT generated by using a suitable target value for each paper (paper type) used at the time of printing. A combination of a specific type of paper (paper type) and a target value corresponding to the paper is referred to as a calibration set.
Generally, the image forming apparatus has a plurality of paper feed stages for simultaneously storing various types of paper. The plurality of paper feed stages is able to store paper classified into different paper types. Suitable paper is fed according to settings at the time of print job execution, and then printing is performed. As described above, the paper type and the output characteristics are closely related with each other.
Japanese Patent Application Laid-Open No. 2011-43815 discusses a technique for presenting, at the time of calibration execution, which paper feed stage stores paper of a paper type to be used at the time of calibration execution.
However, the prior art technique determines, at the time of calibration execution, whether paper of a paper type involving the generation of a correspondent correction table is stored in the apparatus, and presents whether calibration can be executed. Therefore, a user needs to select a paper type involving the generation of a correspondent correction table through the calibration execution.
Further, if calibration for generating a correction table is executed on all of paper types having a target value setting before printing, the processing may take a very long time. Further, if calibration is executed on all of paper types having a target value setting, consumables such as toner and paper may be uselessly consumed.